Known are systems for tracking and displaying person's body positions in motion, which use mechanical means to track positions of a head and body parts--goniometers intended to measure angles of rotation of joints and determine final positions, e.g. of an arm relative to a body, or a finger tip relative to a hand.
The following can be considered as drawbacks of such systems: difficult adjustment of goniometers to human joints, particularly those having a number of freedom degrees, for example--the glenohumeral joints, due to mismatch of the goniometer rotation centres with those of joints rotation. Human joints are not ideal pivots: rotation axes shift when joints rotation angles vary. For improvement of the required accuracy, the appropriate calibrations are to be done.
Also known are magnetic systems for tracking and displaying user's spatial position and orientation (see: Burdea G., Coiffet P./Virtual reality technology, 1994, John Wiley & Sons, Inc., p.p. 17-25). Among these systems are Motion Capture Server manufactured by Polhemus company, and Flock of Birds manufactured by Ascenslon Technology Corp., that comprise a plurality of motion parameters measurement processing plates, a controller, an external synchronisation plate, a communication plate, a keyboard and a monitor, a transmitter comprising three electromagnetic coils, and a plurality of receivers, each of which receivers further includes a triad of electromagnetic minicoils that sense magnetic fields emitted by a transmitter.
Operation range of these systems is not large, the accuracy depends on the distance between a transmitter and a receiver. In a variable magnetic fields system, the presence of foreign metallic articles affects the accuracy due to induction of eddy currents. A constant magnetic fields system is less sensitive to the presence of metallic articles, but the magnetic resistance effect can introduce distortions into the magnetic fields produced by a transmitter.
Moreover, other issues that should be regarded as drawbacks of such systems are an insufficient performance speed as a result of temporal delays in establishing the analogue signal, as well as a high level of noise causing the displayed image to jitter.
Known is an ultrasonic system for tracking the user's spatial position and orientation, comprising a transmitter in the form of a set consisting of three transmitting electroacoustic converters rigidly secured on a support frame, receivers in the form of sets consisting of three microphones rigidly secured on a support frame arranged on a user, e.g. on a helmet having a display, a system for processing a registered information, and a system for displaying a synthesised image for a user (see, ibidem, p.p. 25-28). Locating a user is based on the triangulation principle, and for determining his/her position and orientation, nine measurements of a distance are required to be done. Such system requires a direct sighting line between a system transmitter and receivers. When tracking of a great number of receivers is necessary, the polling rate falls, i.e. the measurements performance speed required for displaying movement of a mobile object and its parts in real time decreases.
The above systems are classified with the systems having sensors for determining the absolute motion parameters, in which systems the absolute position and orientation of a mobile object is measured relative to fixed co-ordinates associated with a transmitter.
Also known are systems having sensors of determination of the relative motion parameters, advantages of which systems consist in simplicity and compactness. "Gloves" used in systems of immersion in virtual reality and having sensors measuring some or all finger joints rotation angles, may be referred to as examples of such systems. Such systems can additionally comprise a sensor for determining absolute three-dimensional movement and orientation (3D-sensor) and used to track movements of user's wrist. Also known is a system that employs optical DataGlove sensors of VPL company (see ibidem, p.p. 33-37) and comprises optical fibres disposed on a light elastic glove, and a 3D-sensor. Its standard configuration uses two sensors attached at the outer side of each finger to perceive bends of main joints. Optical fibres are coupled to an optoelectronic interface. A sensor is designed such that when there is no bending of joints, then the light travelling through a fibre is not weakened, and, vice versa, when there is a bending--the light quantity changes thus allowing to measure a joint rotation angle indirectly. Measurement data are recalculated as angle values using the calibration constants and appropriate approximation equations. A decreased accuracy due to accumulation of errors in the mode of the open kinematic loop, as well as an high cost, can be considered as drawbacks of such systems.
Known is a system of representation of virtual reality for a user, comprising a movable platform unit in the form of a spherical hull with six freedom degrees wherein a user is placed, means for determining position of the spherical hull, a computer installed inside said hull (see U.S. Pat. No. 5,490,784, cl. 434-55, IPC G 09 B 9/00, publ. 13.02.96). A transmitter sends data concerning the platform position to a receiver which in its turn transmits the received data on the angular position of the spherical platform having a user placed therein to a host computer outside the platform. Data on linear movements of such rotoplatform are supplied to the host computer. An on-helmet display tunes a virtual reality image according to the received data on the movements of the platform.
Complexity and an insufficiently high degree of reliability of simulation of the virtual space should be considered as the disadvantages of this known system.
Known is a system for representation for a user of a combined image of real and virtual environments, comprising means for visual display for a user of a composite image; a direction sensor for generating a signal that indicates the user's viewing field direction; a video camera for generating a series of video signals, the combination of which signals represents the user's viewing field; means for positioning a video camera such that its viewing field registers with that of a user and tracks his/her movements; image generation means responsive to the direction signal to generate synthesised signals which characterise a portion of the complete image generated by a computer; means for selecting and combining images to analyse video signals, and selecting video signals or those synthesised by a computer so that to form a composite video signal and send this signal to display means (see: U.S. Pat. No. 5,334,517, cl. 395-129, IPC G 06 F 15/20, publ. 14.10.92).
This known system does not ensure the possibility to provide for a user a virtual environment image that would correspond to changes of the user's position and orientation in the real space.